The present invention relates to an automatic tracking method and a surveying device having tracking function.
As a surveying device for performing measurement of a distance, a horizontal angle, and a vertical angle, a surveying device having tracking function has been known in the past. In this type of surveying device, the surveying device collimates an object reflector (a target) such as a corner cube via a collimating telescope provided on the surveying device, and projects a tracking light via the collimating telescope. Then, the surveying device receives and detects a reflection light from the target via the collimating telescope and when the target moves, detects a deviation between a photodetecting position of the reflection light (from the target) and a collimation center. Based on the deviation, the surveying device adjusts the collimating direction and tracks the target automatically.
Normally, in a surveying device having the tracking function, no operator is assigned on the surveying device side. The target is supported by a surveying operator, or the target is mounted on a construction machine such as a bulldozer. With the progress of the operation, the target moves and the surveying device tracks the moving target.
However, there may be the cases such as: a case where the moving velocity of the target exceeds a speed of the surveying device to follow and the target is deviated out of the field of view of the collimating telescope, or a case where a reflection light from a reflection object such as a windowpane are projected to the surveying device, or a case where a plurality of targets pass each other and reflection lights from two or more targets enter the surveying device, or a case where a vehicle such as an automobile passes in front of the target and the reflection light is interrupted or other cases. In these cases, the surveying device may miss the target out of sight or may recognize the target by error and cannot track the target, and automatic tracking may be interrupted.
Such conditions are caused from the situations that, in case of general type of the collimating telescope, the field angle (view angle) is as small as about 1° and that detection range of the reflection light for automatic tracking is too small.
When the tracking operation is interrupted, the surveying device starts an operation to search the target. In the searching operation, scanning is performed by rotating the collimating telescope in up and down direction and in left-to-right direction in a predetermined range while the tracking light is projected, and the target is detected.
However, the field angle (view angle) of the collimating telescope is as small as about 1° as described above. In order to re-detect the target, it is necessary to have finer scanning pitch and to increase the number of scanning operations. Therefore, when the tracking is interrupted, much time is required until the time when the target is detected again and the tracking can be started. Further, under the working conditions where the optical path is frequently interrupted by obstacles, the problems may arise that the efficiency of the measuring operation is extremely decreased.
In case where the target is extremely deviated from the field of view of the collimating telescope or other case, the target cannot be detected again and the surveying operation itself may be stopped.
A surveying device having tracking function is disclosed in each of JP-A-7-198383, JP-A-2000-346645, and JP-A-2004-170354.